1. Field of the Invention
The present invention relates to oil pressure supply structure in an automatic transmission for supplying oil pressure to a hydraulic servo of a clutch provided in the automatic transmission.
2. Description of the Related Art
A conventional automatic transmission is provided with a plurality of clutches, each clutch including a drum, a piston, a canceller, and so on, as disclosed, for example, in Japanese Patent Application Publication No. JP-A-9-210088 (FIG. 2).
Typically, two or more clutches are provided to achieve a plurality of shift speeds. To make the automatic transmission more compact, the clutches may share components.
In an automatic transmission having a plurality of clutches with shared components, an inner clutch drum is typically splined to an outer clutch drum for rotation integral therewith, and oil pressure is supplied to a hydraulic servo of a clutch housed within the inner drum through oil holes formed in the outside drum and inside drum at equal circumferential intervals.
In the above-described type of automatic transmission, the inner drum is splined to the outer drum at an arbitrary angle during assembly of the automatic transmission. In assembly, variations will occur in the length of the supply path for supplying oil pressure to the hydraulic servo of the clutch housed in the inner drum through first and second oil holes due to differences in their relative angular orientation, and as a result of this variation, differences occur in the time required to supply the oil pressure to the hydraulic servo, leading to variation in the clutch engagement time as between different individual transmissions. In a transmission provided with four circumferentially spaced first oil holes 65 and four circumferentially spaced second oil holes 66, as shown in FIG. 10A, the maximum angular spacing (phase shift) between the first oil holes 65 and second oil holes 66 will be 45 degrees, and hence the length of the supply path for supplying oil pressure to the hydraulic servo will be greater than that of a case in which the angular orientations (phases) of the first oil holes 65 and second oil holes 66 are the same (0 phase shift), leading to a delay in the clutch engagement time. Likewise, where the first oil holes 65 and the second oil holes 66 are each 6 in number the maximum angular spacing will be 30° as shown in FIG. 10B.
To eliminate this variation in the clutch engagement time, the second oil holes 66 may be positioned in alignment with the first oil holes 65 when matching the inner drum within the outer drum, but such positioning requires marking the drums thereby adding a troublesome task to the assembly process and leading to an increase in cost.